Wafer alignment device

Abstract

Zone plate alignment aids on a mask and semiconductor wafer are used in a projection type system for aligning the wafer and mask prior to transfer of a circuit pattern from the mask to the wafer in an exposure process. The condenser system includes an aperture in the shape of a chevron or other convenient alignment pattern while the viewing system of the device is provided with a complementary shaped pupil stop. The condenser aperture and the viewing system stop cofunction to enhance the image contrast seen through the viewing system.

What is claimed is: 
     
       1. A device for aligning a wafer with a mask prior to an exposure process with a projection system during which a circuit pattern is transferred from the mask to the wafer, said device comprising, in combination: a first alignment pattern in the form of a zone plate on a surface of said mask;   a second alignment pattern in the form of a zone plate on a surface of said wafer;   a light source;   condenser means disposed between said light source and said mask for illuminating said first and second alignment patterns, said condenser means including a pupil aperture with a transparent region of predetermined shape;   projection means disposed between said mask and said wafer for projecting the mask pattern onto the wafer; and   viewing means for monitoring condenser pupil images formed by the mask and wafer zone plate patterns, said viewing means including a viewing system aperture with an opaque region geometrically similar to said transparent region.   
     
     
       2. The device defined in claim 1 wherein said condenser means includes an aperture shaped to enhance or facilitate its alignment capability. 
     
     
       3. The device defined in claim 2 wherein said viewing system includes a beam splitter in said projection system and an objective lens receiving light from said beam splitter. 
     
     
       4. The device defined in claim 1, further comprising control means operatively connected to said viewing means and said wafer or mask for automatically adjusting the relative position of the wafer and mask in response to images detected by said viewing system. 
     
     
       5. The device defined in claim 1 wherein said transparent region is in the form of a chevron. 
     
     
       6. The device defined in claim 1 wherein said transparent region is in the form of a circle divided into two areas by an opaque chevron shaped region. 
     
     
       7. A method for aligning a wafer with a mask during an integrated circuit manufacturing process, said method comprising the steps of: providing said mask with a first alignment aid in the form of a zone plate;   providing said wafer with a second alignment aid in the form of a zone plate;   generating an illumination light bundle having a predetermined transparent pattern in its pupil;   optically transmitting said bundle through a portion of said mask including said first alignment aid;   focusing said pattern onto a first image plane at a point proximate to said first alignment aid;   projecting radiation of said bundle, upon transmission thereof through said mask, onto a portion of said wafer including said second alignment aid;   diffractively reflecting radiation from said second alignment aid to form on a second image plane an image geometrically similar to said pattern;   optically transmitting images of said pattern from said first and said second image plane to an image detector through an aperture having an opaque region geometrically similar to said pattern; and   adjusting the relative position of said mask and said wafer in response to the relative position of said images at said detector.   
     
     
       8. The method defined in claim 7, further comprising the steps of: providing said mask with a third alignment aid in the form of a zone plate;   providing said wafer with a fourth alignment aid in the form of a zone plate; and   aligning targets formed by said third and said fourth alignment aid.   
     
     
       9. The method defined in claim 7 wherein the step of adjusting the relative position of said mask and wafer in response to said images is accomplished automatically. 
     
     
       10. The method defined in claim 7 wherein said first alignment aid includes a pair of zone plates, said bundle being transmitted through a portion of said mask including both zone plates of said pair, said pattern being focused by each of the zone masks of said pair onto said first image plane.